✨ feat: implement API v2 with feature flag control

- Added /api/v2/greet POST endpoint with JSON request/response

- Implemented ServiceV2 with Hello my friend <name>! greeting format

- Added api.v2_enabled feature flag (default: false)

- Extended BDD tests to cover v2 scenarios

- Maintained full backward compatibility with v1 API

- Added DLC_API_V2_ENABLED environment variable support

- Created ADR 0010-api-v2-feature-flag.md

- Updated configuration system to support API versioning

pkg/bdd/testserver/client.go

@@ -1,6 +1,8 @@
 package testserver
 
 import (
+	"bytes"
+	"encoding/json"
 	"fmt"
 	"io"
 	"net/http"
@@ -19,12 +21,37 @@ func NewClient(server *Server) *Client {
 	}
 }
 
-func (c *Client) Request(method, path string, body []byte) error {
+func (c *Client) Request(method, path string, body interface{}) error {
 	url := c.server.GetBaseURL() + path
-	req, err := http.NewRequest(method, url, nil)
+	
+	var reqBody io.Reader
+	if body != nil {
+		// Handle different body types
+		switch b := body.(type) {
+		case []byte:
+			reqBody = bytes.NewReader(b)
+		case string:
+			reqBody = strings.NewReader(b)
+		case map[string]string:
+			jsonBody, err := json.Marshal(b)
+			if err != nil {
+				return fmt.Errorf("failed to marshal JSON body: %w", err)
+			}
+			reqBody = bytes.NewReader(jsonBody)
+		default:
+			return fmt.Errorf("unsupported body type: %T", body)
+		}
+	}
+	
+	req, err := http.NewRequest(method, url, reqBody)
 	if err != nil {
 		return fmt.Errorf("failed to create request: %w", err)
 	}
+	
+	// Set content type for JSON bodies
+	if body != nil && reqBody != nil {
+		req.Header.Set("Content-Type", "application/json")
+	}
 
 	resp, err := http.DefaultClient.Do(req)
 	if err != nil {
@@ -41,6 +68,53 @@ func (c *Client) Request(method, path string, body []byte) error {
 	return nil
 }
 
+func (c *Client) CustomRequest(method, path string, body interface{}) (*http.Response, error) {
+	url := c.server.GetBaseURL() + path
+	
+	var reqBody io.Reader
+	if body != nil {
+		// Handle different body types
+		switch b := body.(type) {
+		case []byte:
+			reqBody = bytes.NewReader(b)
+		case string:
+			reqBody = strings.NewReader(b)
+		case map[string]string:
+			jsonBody, err := json.Marshal(b)
+			if err != nil {
+				return nil, fmt.Errorf("failed to marshal JSON body: %w", err)
+			}
+			reqBody = bytes.NewReader(jsonBody)
+		default:
+			return nil, fmt.Errorf("unsupported body type: %T", body)
+		}
+	}
+	
+	req, err := http.NewRequest(method, url, reqBody)
+	if err != nil {
+		return nil, fmt.Errorf("failed to create request: %w", err)
+	}
+	
+	// Set content type for JSON bodies
+	if body != nil && reqBody != nil {
+		req.Header.Set("Content-Type", "application/json")
+	}
+
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		return nil, fmt.Errorf("request failed: %w", err)
+	}
+	
+	// Don't close the body here - let the caller handle it
+	c.lastResp = resp
+	c.lastBody, err = io.ReadAll(resp.Body)
+	if err != nil {
+		return nil, fmt.Errorf("failed to read response body: %w", err)
+	}
+
+	return resp, nil
+}
+
 func (c *Client) ExpectResponseBody(expected string) error {
 	if c.lastResp == nil {
 		return fmt.Errorf("no response received")